In a conventional decanter type centrifugal separator 100 shown in FIG. 10, during separation and dehydration treatment of crystalline particles, such as those of PVC (polyvinyl chloride), terephthalic acid, or the like, or starch ground milk, or the like, when a throughput thereof increases during the conveyance and dehydration treatment of centrifugally precipitated particles (solid) along an axial direction thereof through a minute difference in speeds between a bowl 120 and a screw conveyor 140 disposed therein, chattering (torsional self-excited vibration) of the screw conveyor 140 is generated between the bowl 120 and a tip of a screw conveyor flight 142 through the treatment substances. As a result, there may be problems including damage of an internal gear due to an impact load (torque) being imposed on a differential gear unit 150, and a crack in a stock solution feed hole part 144 at 45 degrees due to a torsion of a screw conveyor cylindrical hub 141 (boss). Accordingly, the throughput of the conventional decanter type centrifugal separator 100 is restricted to less than approximately half of an intended design maximum treatment capacity thereof.
To eliminate such problems, proposals have been disclosed in, for example, U.S. Pat. No. 4,069,967 (Jan. 24, 1978), U.S. Pat. No. 4,069,966 (Jan. 24, 1978), and U.S. Pat. No. 3,685,722 (Aug. 22, 1972). Apparatuses disclosed in the references provide flexibility in a direction of rotation on a side of a differential gear unit in order to absorb torsional self-excited vibrations. However, plays may be created in the differential gear unit or in connection parts at both ends of a drive force transmission shaft disposed between the differential gear unit and a screw conveyor. As a result, it is difficult to absorb the torsional vibrations generated in the conveyor at each transmission part.
More specifically, in U.S. Pat. No. 4,069,967, a torsion bar, or the like, is mounted to a pinion gear shaft on an input side of the differential gear unit for absorbing the torsional vibration. Although maintaining spring characteristics, the torsion bar itself has an extremely small damping factor. Accordingly, it is insufficient for absorbing the torsional vibration. Further, the apparatus is mounted to the pinion gear shaft on the input side of the differential gear unit. Accordingly, it is easily expected that backlashes (plays) of the respective gears constituting a drive force transmission path in the differential gear unit, or plays of, for example, spline teeth of connection parts at both ends of a transmission shaft between the differential gear unit and a screw conveyor may accumulate. As a result, the effect of absorbing the torsional vibration generated in the conveyor in each transmission part may decrease.
In U.S. Pat. No. 4,069,966, a torsion bar is mounted to a pinion gear shaft on an input side of a differential gear unit in the same way as above. Further, as an auxiliary mechanism, a cantilever torsion bar tip part on the pinion gear shaft is immersed in viscous liquid to improve a damping factor for absorbing the torsional vibration. However, similar to the apparatus above, the apparatus is mounted to the pinion gear shaft on the input side of the differential gear unit. Accordingly, it is easily expected that backlashes (plays) of the respective gears constituting a drive force transmission path in the differential gear unit, or plays of, for example, spline teeth of connection parts at both ends of the transmission shaft between the differential gear unit and a screw conveyor may accumulate. As a result, the effect of absorbing the torsional vibration may decrease.
In U.S. Pat. No. 3,685,722, an output shaft side (a screw conveyor side) of a differential gear unit is provided with flexibility in a direction of rotation for absorbing the torsional self-excited vibration. However, a drive force is transmitted through connection parts at both ends of a transmission shaft between the differential gear unit and a screw conveyor. Accordingly, it is easily expected that plays of, for example, spline teeth of connection parts at both ends of the transmission shaft may accumulate. As a result, the effect of absorbing the torsional vibration may decrease. In addition, basically, a normal coil spring is combined with a leaf spring to provide the flexibility. Accordingly, it is supposed that a damping factor is low, and the effect of absorbing the torsional vibration is low.